The invention is generally directed to a composite tape for use in cable manufacture. In particular, the invention provides a multifolded composite tape constructed in a single tape configuration with a multiple of longitudinal channels or grooves for wrapping and shielding individual insulated conductors. The invention also provides methods of making a multifolded composite tape as a single tape configuration. The invention further provides a communications cable comprising a multifolded composite tape for separating and shielding one or more conductors.
High-speed data communications cables currently in use include pairs of insulated conductors twisted together to form a two-conductor group or a transmission line. Such pairs of insulated conductors are commonly referred to in the art as xe2x80x9ctwisted pairsxe2x80x9d. Multiples of twisted pairs are typically bundled or closely spaced together within high-speed data cables. Such close proximity between twisted pairs often causes electrical energy to transfer from one twisted pair to other adjacent twisted pairs coexisting within a cable. This transfer of electrical energy between twisted pairs is a phenomenon known as crosstalk, which interferes and degrades electrical signals and data transmission. Twisted pairs must, therefore, be sufficiently separated physically and shielded electrically in order to reduce and isolate crosstalk.
Crosstalk presents a particular problem in high frequency applications wherein as the frequency of transmission increases, crosstalk increases logarithmically. Thus, the need to shield twisted pairs increases with the need for greater transmission speed. For instance, a category 7 cable used for relatively high speed data transmission is required to meet specific performance standards for crosstalk isolation established by third party testing organizations. Therefore, in order to meet such performance standards, while providing greater transmission speed and throughput, methods of shielding and isolating twisted pairs become important for maintaining the quality of data transmission.
Various prior art methods attempt to meet standards for crosstalk isolation in high-speed data communications cable and include techniques and cable designs for physically separating twisted pairs and maintaining twisted pairs in fixed positions. In addition, prior art methods include individually shielding twisted pairs to insulate twisted pairs from crosstalk. Such shielding techniques typically include various techniques and shielding tapes for tape wrapping individual twisted pairs prior to cabling. Typically, tape wrapping involves wrapping a metal or metallized tape longitudinally or helically around a twisted pair. Such tape wrapping techniques cause a portion of the metal or tape to overlap upon itself as it is wound around the twisted pair to achieve a continuous wrap. The result is that areas along the twisted cable face a metal-to-nonmetal portion of the wrapping tape at the site of a tape overlap. Typically, shielding or wrapping tape comprises a conductive, often metallic, surface and a dielectric film, often plastic, surface such that the overlap created is a metal-to-film interface. Such overlaps are susceptible to signal leakage, interference and signal degradation as well as contribute to crosstalk between adjacent twisted pairs and proximate cables. In addition, individually wrapping twisted pairs is a lengthy operation and an additional step in manufacturing twisted pairs.
Therefore, it is desirable to provide a shielding tape and techniques for individually wrapping twisted pairs prior to cabling that overcomes the problems associated with the prior art described above. Such a shielding tape and techniques would reduce or eliminate the negative effects upon electrical properties and conductor performance associated with tape overlap and more particularly would isolate crosstalk. In addition, it is desirablc to provide a communications cable comprising a shielding tape for physically separating and electrically isolating individual insulated conductors contained therein to substantially reduce crosstalk between adjacent conductors situated within the cable as well as between the cable and other proximately located communications cables.
According to the invention, a multifolded composite tape is provided to better facilitate isolation and electrostatic shielding of multiple pairs of insulated conductors of a high-speed data transmission cable that is required to meet the need for greater speed, throughput and quality of signal and data transmission. The multifolded composite tape of the invention is constructed as a single tape configuration having a robust shielding construction to compartmentalize and encapsulate individual pairs of insulated conductors (referred to herein as xe2x80x9ctwisted pairsxe2x80x9d) during cable manufacture. The composite tape of the invention has the benefit of using a single tape configuration that completely wraps, electrically shields, and isolates individual twisted pairs to achieve a desired crosstalk performance.
The multifolded composite tape of the invention resolves many of the problems associated with individually wrapping twisted pairs to achieve greater consistency of electrical properties and electrical performance. In addition, the various single tape configurations of the invention increase manufacturing productivity by reducing the amount of tape required to wrap individual twisted pairs and increasing production speed. In addition, the single tape configurations provide greater strength, thereby reducing the incidence of tape break during-cable manufacture. The single tape design also provides a more consistent geometry that imparts consistency and predictability with respect to electrical properties and cable performance.
The multifolded composite tape of the invention also provides a number of embodiments comprising a variety of single tape configurations to simultaneously wrap and completely encapsulate a multiple of twisted pairs during cable manufacturing. The single tape configurations generally comprise one or more metallic foil/plastic film laminates that are folded and assembled to form a multiple of channels or grooves for containing twisted pairs.
Embodiments of the single tape configuration according to the invention comprise one or more laminates assembled into a single tape. Each laminate is constructed of at least one layer or sheet of a first material, such as a conductive material, bonded to at least one layer or sheet of a second material, such as an insulating dielectric material, to form a single laminate. The single laminate is a basic component of the various single tape configurations according to the invention. The construction of the laminate as described herein does not limit the invention to a single layer of conductive material, such as a metallic foil, bonded to a single layer of dielectric material, such as a plastic or polyester film, but contemplates other laminate constructions comprising more than one layer or sheet of conductive material and/or more than one layer or sheet of dielectric material. In addition, the invention is not limiting with respect to the materials of construction of the laminate layers and contemplates other materials in addition to a metallic foil and plastic or polyester film.
In a first embodiment of the invention, a single tape configuration comprises four metallic foil/film laminates folded and assembled to form a single tape configuration having an X-shaped cross-section or profile that forms or defines four channels or grooves extending longitudinally along a length of the single tape. Each laminate is constructed of at least one layer or sheet of metallic foil bonded to at least one layer or sheet of thin plastic film to form a metallic foil/film laminate. During assembly of the single tape configuration, the foil/film laminates are folded and/or bonded such that the foil layers of the laminates are oriented to face or define the four channels or grooves. The single tape configuration which results comprises four fin-like shield members extending radially from a center axis or vertical center line and longitudinally along the length of the tape to form or define the four channels or grooves. Each shielding member has an internal portion of dielectric material disposed between conductive material.
Each channel or groove is of sufficient size to lay at least one twisted cable therein. During cable manufacturing, four twisted pairs are laid in the X-shaped single tape configuration and therein simultaneously wrapped by utilizing one or more forming dies. The foil layer facing each channel or groove essentially provides a continuous longitudinal foil-to-foil wrap in which a twisted pair is encapsulated. The foil-to-foil wrap physically separates and electrically shields the twisted pair by achieving a continuous and closed conductive shield. The resultant foil-to-foil contact achieved avoids the problems associated with foil-to-film overlap produced during individually wrapping twisted pairs.
In a second embodiment of the invention, a single tape configuration comprises at least one metallic foil/film laminate accordion-folded to form a single tape configuration having a cross-section or profile that forms or defines one or more channels or grooves extending longitudinally along a length of the single tape. The metallic foil/film laminate is similarly constructed as described above with respect to the foil/film laminates of the first embodiment. The metallic foil/film laminate is accordion-folded lengthwise into a multiple of pleats to achieve a single tape configuration having an accordion cross-section or profile. Each pleat can be of a substantially equal width. Each pleat includes a foil layer on a first side and a film layer on a second opposite side. During formation of the multiple of accordion pleats, each pleat having the film layer folded therein is fused or bonded to seal the pleat. The foil/film laminate is accordion-folded lengthwise until a desired number of pleats is achieved. The number of pleats created is related to the number of channels or grooves required. Thereafter, the single tape configuration is opened by unfolding the pleats having the foil layer folded therein and wrapping the single tape back upon itself such that the foil layer is oriented to face or define one or more channels or grooves. The single tape configuration which results comprises two or more fin-like shield members extending radially from a center axis or vertical center line and longitudinally along the length of the single tape to form or define the one or more channels or grooves. The single tape configuration of the second embodiment provides the flexibility to provide as many channels and grooves as may be required to wrap any number of twisted pairs contained within a particular cable design.
In a third embodiment of the invention, a method is provided for making a composite tape for use in cable manufacture, the method comprising providing a first laminate of at least one layer of conductive material bonded to at least one layer of dielectric material; folding the first laminate conductive material-to-conductive material to form an interface of conductive material; providing a second folded laminate constructed and folded similar to the first folded laminate; butting the first and second folded laminates fold-to-fold; providing a third laminate and a fourth laminate, the third laminate and the fourth laminate each having at least one layer of conductive material bonded to at least one layer of dielectric material; bonding the layer of dielectric material of the third laminate to a first plane of dielectric material formed by the dielectric material of the butted first and second folded laminates; bonding the layer of dielectric material of the fourth laminate to a second opposing plane of dielectric material formed by the dielectric material of the butted first and second folded laminates; and opening the conductive material interfaces to form a plurality of fin-like shielding members that extend radially from a center axis and longitudinally along a length of the laminates to define a plurality of channels.
In a fourth embodiment of the invention, a method is provided for making a composite tape for use in cable manufacture, the method comprising providing a laminate of at least one layer of conductive material bonded to at least one layer of dielectric material, the laminate having a length and a width; folding the laminate along its length repeatedly to form a multiple of longitudinal accordion pleats, each pleat having either a dielectric material interface or a conductive material interface disposed therein; bonding the dielectric material interfaces; and opening the conductive material interfaces to form a plurality of fin-like shielding members extending radially from a center axis and longitudinally along the length of the laminate to define a plurality of channels.
In a fifth embodiment of the invention, a communications cable is provided comprising a tubular jacket; a composite tape contained within the jacket including two or more fin-like shielding members joined at a center axis, each shielding member extending radially from the center axis and longitudinally along a length to define two or more channels, each shielding member having an internal portion of a first material disposed between portions of a second material; and at least one twisted pair of insulated conductors disposed in each of the channels.
In a sixth embodiment of the invention, a communications cable is provided comprising a tubular jacket and a composite tape constructed according to the method of the invention as described with respect to the fourth embodiment. The composite tape is contained within the jacket and includes two or more fin-like shielding members joined at a center axis, each shielding member extending radially from the center axis and longitudinally along a length to define two or more channels, each shielding member having an internal portion of a first material disposed between portions of a second material; and at least one twisted pair of insulated conductors disposed in each of the channels.